The present invention relates to the electrification of office furniture and the like, and in particular to a modular power distribution system therefore.
Modular furniture units such as for example wall panels are widely used in architectural design, especially for commercial establishments, because of the advantages they provide in ease of installation, convenience of rearrangement of floor plans after installation, attractiveness of appearance, etc. One problem encountered in the use of modular wall panels is the provision of adequate electrical power for the areas enclosed by the panels while still retaining the advantage of flexibility in the location of the panels. This problem has been answered to some extent in prior power distribution systems disclosed, for example, in U.S. Pat. Nos. 4,060,294, issued Nov. 29, 1977 and related U.S. Pat. Nos. 4,370,008, issued Jan. 25, 1983 and 4,199,206, issued Apr. 22, 1980.
In the system of the above-referenced patents, identical power blocks are secured within the bottom edge of each panel unit adjacent the opposite ends thereof. The power blocks are interconnected by three conductors running the length of the panel within the bottom edge and are adapted to receive, on either of their opposite vertical faces, panel-to-panel jumper connectors or a power-in connector through which power is supplied by a three-conductor cable from a branch circuit of the base power distribution system. The power blocks are further adapted to receive, on either vertical face, a duplex outlet connector through which outlet power is available to the areas enclosed by the panels. By these means, a duplex outlet may be provided at each of the opposite ends of a panel unit, and on both sides thereof, along the length of an indefinite run of panel units, limited by the permissible number of outlets that can be connected to a single branch circuit. When the number of outlets installed along a panel run has reached the permissible limit, it is necessary to break the continuity of the system and to begin a new run from a separate power-in connector leading from a different branch circuit of the power main.
Improvements over the three-wire power distribution system for modular panels have been devised to enable the installation of longer panel runs and the placement of a greater number of duplex outlets therein with fewer power-in connections from separate branch lines of the base power distribution system. Such improved systems are exemplified by the systems disclosed in U.S. Pat. Nos. 4,313,646, issued Feb. 2, 1982; 4,367,370, issued Jan. 4, 1983; and 4,740,167, issued Apr. 26, 1988. The systems of U.S. Pat. Nos. 4,367,370 and 4,740,167 employ power blocks at opposite ends of a panel unit which are adapted to receive connectors for panel-to-panel jumper cables, connectors for cables interconnecting the power blocks of a panel unit and for power-in cables, and duplex outlet connectors on the opposite vertical faces. In the system of U.S. Pat. No. 4,313,646, the power blocks are formed integrally with a single duplex outlet.
The feature in common of the '646, '370 and '167 patents is that each of the systems is supplied power through, and the power blocks are interconnected by, a five-wire cable. The base power distribution system may suitably comprise a three-phase system and the five wires provide three lines, one shared neutral and one safety ground. The duplex outlets may be selectively connected between any one of the three available lines and neutral. The five-wire panel distribution systems enable the installation of panel runs having more than one circuit within a panel.
To overcome the limitation imposed by the load capacity of a shared neutral conductor, U.S. Pat. No. 4,781,609, issued Nov. 1, 1988, discloses a seven-wire power distribution system for modular panels providing three lines, three neutrals, one for each of the available lines, and one safety ground.
Increasing the number of conductors in a power distribution system for a panel originally designed to accommodate a three-wire power distribution system presents a challenge as to the manner in which the additional number of conductors are to be fitted into the available space. In the system of U.S. Pat. No. 4,781,609, the power blocks contain seven vertically aligned, parallel conductive plates. Each of the plates is formed with prongs projecting outwardly from both sides of the plate and with two prongs spaced conductors. Thus, these outlets accommodate a limited number of connection variations. The problems resulting from the limited number of connection variations and the limited versatility afforded by known outlets are particularly exacerbated if the power outlets are to be capable of selecting a supply circuit from a power block having more than seven wires installed within the limited confines of existing three-wire raceways.